1. Field of the Invention
The present invention relates to a device for projecting an image, in particular, but not exclusively, to a device for projecting an image of increased brightness and/or of increased size, wherein the image can be projected as a 2-D image or a 3-D image.
2. Description of the Related Art
A MEMS micro-mirror device is a device that contains a Micro-Electrical-Mechanical-System with a reflective surface. The optical MEMS may comprise a cylindrical, elliptical, rectangular or square micro-mirror that is adapted to move and to deflect light over time. The micro-mirror is connected by suspended arms to a fixed part and can tilt and oscillate along one or two axis. For example it can oscillate vertically and horizontally. Different actuation principles can be used, including electrostatic, thermal, electro-magnetic or piezoelectric. MEMS devices are known in which the area of these micro-mirrors are around a few mm2. In this case, the dimensions of the MEMS device, comprising the packaging, is around ten mm2. This device is usually made of silicon, and can be encapsulated in a package that can include the driving actuation electronics. Various optical components, such as for example lenses, beam combiner, quarter-wave plates, beam splitter and laser chips, are assembled with the packaged MEMS to build a complete device.
A typical application of the MEMS micro-mirror devices is for projection devices. In a projection device, a 2-D image or a video can be displayed on any type of surface. In a color device, each pixel is generated by combining modulated red, green and blue laser light sources, by means of, for example, a beam combiner. A MEMS micro-mirror device directs the light of the laser light source to a projection surface and reproduces the image, or the video, pixel-by-pixel. By means of its oscillations, the micro-mirror within the device will continuously scan from left to right and from top to bottom, or according to a different trajectory including e.g., Lissajou trajectories, so that each pixel of the 2-D image is displayed on the screen.
Typically, the micro-mirror of a MEMS micro-mirror device is able to oscillate along one axis. Therefore, in order to display a 2-D image on a screen a projection device will require two MEMS micro -mirror devices; a first MEMS micro-mirror device is required to deflect light along the horizontal image axis and a second MEMS micro-mirror device is required to deflect light along the vertical image axis. During operation, the micro-mirror of the first MEMS micro-mirror device receives light from the beam combiner and deflects the light to the micro-mirror of the second MEMS micro-mirror device. The micro-mirror of the second MEMS micro-mirror device will in turn deflect the light to the display surface where it will appear as a pixel. The micro-mirror of the first MEMS micro-mirror device will oscillate to scan the light along the horizontal image axis thereby displaying the first row of pixels on the display surface. The micro-mirror of the second MEMS micro-mirror device will oscillate about its oscillatory axis so that light received from the micro-mirror of the first MEMS micro-mirror device is scanned along the vertical image axis. The combined effect of the oscillating micro-mirrors is that the light from the beam combiner is scanned in a zig-zag or raster pattern along the display surface. The process is continuous so that a complete image is visible to the viewer on the display surface. The first and the second MEMS micro-mirror devices are precisely positioned such that the oscillatory axes of the respective micro-mirrors are orthogonal; this ensure that all the light received by the micro-mirror of the first MEMS micro-mirror device will be deflected to the micro-mirror of the second MEMS micro-mirror device as the micro mirrors oscillate.
Other MEMS micro-mirror devices comprise a micro-mirror which can oscillate along two orthogonal axes. Such a micro-mirror can scan the light beam in two dimensions. Therefore, to display a 2-D image on a display surface a single mirror will oscillate about two axes to scan the light in a zig-zag, Lissajou or raster pattern over the display surface. Various methods of oscillating the micro-mirrors are employed. For example, an electrostatic means; thermal means; electro-magnetic means, or piezoelectric means.
Projection devices in general are used to project images or videos onto a display surface. The quality of the image projected by a projection device is dependent on the brightness of the image; in contrast to a bright image, the detail of a dull image will not be visible when projected on the display surface. Accordingly it is advantageous to display a bright image on the display surface so that the detail of the image will be visible. However, in projection devices the brightness of the image projected on the display surface is limited by the brightness of the light which can be provided by the light source of the projection device. The brightness of the light which can be provided by a light source is limited by the electrical capabilities of the light source (e.g., the wattage of a light-bulb, LED or laser diode in the light source). Consequently, there exists a maximum brightness at which a projection device can display an image. There is a need in the art for a means and method which will enable increasing the brightness of an image which does not require modification of the projection device.
The dimensions of an image projected by a projection device onto a display surface are also limited. To increase the size of the image projected onto a display surface requires adjustment of a focus lens of the projection device such the light corresponding to each pixels is spread over a larger area of the display surface. Increasing the size of the image will compromise the quality of the image as the sharpness, the pixel density and the brightness of the image will decrease. There is a need in the art for a means and method for enabling enlargement of a projected image without compromising the quality of the image.
Additionally, there is a need in the art for a simplified means which will enable increasing the brightness of an image and/or enabling enlargement of a projected image.
US20090257031 discloses the use of a microprocessor to physically move two projectors so that their projected images are aligned on the display screen. Precise positioning of the projectors relative to one another is difficult to achieve. Furthermore, the device of US20090257031 requires that the projectors are connected by means of a linkage so as to allow the microprocessor to position the projectors relative to one another to achieve the desired alignment of images. Thus, the device disclosed in US20090257031 does not permit the projectors to be independent from one another.
It is an aim of the present invention to obviate or mitigate one or more of the aforementioned disadvantages.